The crew reported that they felt no jarring when the vessel struck the middle dolphin, but the wharf operator felt a jerky movement in the dolphin. A conventional wharf will absorb more of the impact from a vessel striking it than will a dolphin mounted on piles. It is possible that the crew felt no jarring from the impact due to the low approach speed of the vessel. Before the tanker arrived, the two unloading arms were secured in place. As no Hydro-Qubec mechanic was on duty on the wharf and the hydraulic system had not been started up, the only event that could have caused the securing mechanism of the unloading arm to release and the unloading arm to move was jarring caused by impact. The design of the securing mechanism is such that the lock screw lever does not remain in position on the coupling ball if the lock screw is not tightened. The lever must be raised in order to engage it on the coupling ball of the unloading arm. For the securing mechanism of the upstream unloading arm to release without being damaged, the lock screw must not have been tight enough. The square-head lock screw of the upstream unloading arm was more difficult to tighten than the wing-head lock screw of the downstream unloading arm. In addition, the berthing manoeuvre consisted of bringing the port side of the vessel into contact with the face of the middle dolphin, then slipping the vessel into position alongside the three dolphins. However, the rubber scuff marks on the port shoulder and the damage to the ship's fender indicate that the ship pressed against the downstream oblique corner of the fender. Therefore, before slipping alongside the dolphin, the vessel glanced off the downstream corner of the dolphin. As the hydraulic system was not in operation, the north-east wind blew the unloading arm outward.Analysis The crew reported that they felt no jarring when the vessel struck the middle dolphin, but the wharf operator felt a jerky movement in the dolphin. A conventional wharf will absorb more of the impact from a vessel striking it than will a dolphin mounted on piles. It is possible that the crew felt no jarring from the impact due to the low approach speed of the vessel. Before the tanker arrived, the two unloading arms were secured in place. As no Hydro-Qubec mechanic was on duty on the wharf and the hydraulic system had not been started up, the only event that could have caused the securing mechanism of the unloading arm to release and the unloading arm to move was jarring caused by impact. The design of the securing mechanism is such that the lock screw lever does not remain in position on the coupling ball if the lock screw is not tightened. The lever must be raised in order to engage it on the coupling ball of the unloading arm. For the securing mechanism of the upstream unloading arm to release without being damaged, the lock screw must not have been tight enough. The square-head lock screw of the upstream unloading arm was more difficult to tighten than the wing-head lock screw of the downstream unloading arm. In addition, the berthing manoeuvre consisted of bringing the port side of the vessel into contact with the face of the middle dolphin, then slipping the vessel into position alongside the three dolphins. However, the rubber scuff marks on the port shoulder and the damage to the ship's fender indicate that the ship pressed against the downstream oblique corner of the fender. Therefore, before slipping alongside the dolphin, the vessel glanced off the downstream corner of the dolphin. As the hydraulic system was not in operation, the north-east wind blew the unloading arm outward. The port shoulder of the vessel struck the downstream corner of the middle dolphin. The striking of the vessel shook the dolphin which was mounted on piles. The lock screw of the securing mechanism of the unloading arm was not tight enough on the coupling ball. The jarring released the lock screw from the coupling ball and, under the pull of gravity, the lever fell, thereby releasing the unloading arm. With no pressure in the hydraulic system and with the force of the wind against it, the unloading arm extended outward. The unloading arm fell on the bulwark rail of the ship as she slipped alongside the dolphin. The crew was unable to clear the unloading arm from the bulwark before it reached the rigging of the landing boom. The seaman's hand was crushed between the unloading arm and a landing boom guy wire.Findings The port shoulder of the vessel struck the downstream corner of the middle dolphin. The striking of the vessel shook the dolphin which was mounted on piles. The lock screw of the securing mechanism of the unloading arm was not tight enough on the coupling ball. The jarring released the lock screw from the coupling ball and, under the pull of gravity, the lever fell, thereby releasing the unloading arm. With no pressure in the hydraulic system and with the force of the wind against it, the unloading arm extended outward. The unloading arm fell on the bulwark rail of the ship as she slipped alongside the dolphin. The crew was unable to clear the unloading arm from the bulwark before it reached the rigging of the landing boom. The seaman's hand was crushed between the unloading arm and a landing boom guy wire. The crew was unable to clear the unloading arm before it struck the rigging of the landing boom. The crew member's hand got stuck between the unloading arm and the guy wire. The striking of the vessel against the dolphin shook the unloading arms, and a securing mechanism that was not tight enough released. Because of the wind pushing against it, the unloading arm extended outward.Causes and Contributing Factors The crew was unable to clear the unloading arm before it struck the rigging of the landing boom. The crew member's hand got stuck between the unloading arm and the guy wire. The striking of the vessel against the dolphin shook the unloading arms, and a securing mechanism that was not tight enough released. Because of the wind pushing against it, the unloading arm extended outward. To prevent the unloading arms from falling if they are jarred loose, safety chains have been installed.Safety Action Taken To prevent the unloading arms from falling if they are jarred loose, safety chains have been installed.